1. Field of the Invention
The invention relates to the field of apparatus and method for using light emitting diodes (LED) or other light sources of similar or differing wavelengths in an approximately unitized beam. The device would be generally described as being in the field of fiber illumination, but could be used in non-fiber devices in the general lighting field as well.
2. Description of the Prior Art
The initial investment cost of LED illumination is very expensive when compared with traditional lighting means using cost per lumen as the metric. While this may change over time, this high cost places a premium on collection and distribution efficiency of the LED optical system. The more efficient the system, the better the cost/benefit comparison with traditional illumination means, such as incandescent, fluorescent and neon.
A popular type of illumination device is the fiber illuminator. Typically these devices comprise an illumination source, a reflector and/or lens and a means to attach the optical fiber in place. Illumination sources used in these devices range from incandescent (Halogen, etc.) to HID (High-Intensity-Discharge arc lamps). The LED is relatively new to these devices, but holds several advantages. The light energy of the LED is primarily in the visible spectrum and contains little or no UV or IR. Therefore LEDs do not cause deterioration of the fiber as do the traditional means. LEDs also provide color(s) at a very improved efficiency.
However, the optical performance of conventional Fiber Devices, with or without LEDs, is often less than satisfactory. For example, For an HID lamp to provide red output requires filtering of all the other colors in the beam spectrum. This can result in over 50% efficiency loss. Prior art techniques in LED technology suffer a different problem, however. Most LED fiber-illumination devices use one of three basic techniques. Butt-joining the LED to the fiber, imaging the LED emitter onto the fiber end with a ball or other lens and elliptical reflectors. An LED is a Lambertian emitter. Therefore, in the first example, only the energy of the LED that is within the numerical aperture (N/A) of the fiber is accepted, the rest is rejected as loss to the device. In the second example only the energy from the LED that falls within the N/A of the lens system is accepted. In a reflector based system, only a single LED can be collected at high efficiency, so the device is limited in scope.
Another class of prior art includes the ability to change color by placing a color wheel in way of the beam before it enters the fiber. Typically, these dichroic color wheels are manufactured of glass to handle the high temperature of the light source.
Another form of color illuminator combines red, green, blue and possibly other colored light sources, either LED or not, in order to increase brightness in a complex dichroic mirrored optical path to combine the resultant light. Again the optical path ways are long, the optical system is necessarily physically large and the overall performance is still subject to intensity and collimation losses.
What is needed is a some kind of a controllable combined light source which is not subject to the inherent disadvantages of such prior art.